I am very new to epubs and trying to learn how it works. I was accessed to examine a clients epub that would not validate and it shows that it was created in calibre and with word. I was trying to learn the structure but I am getting an error and I dont know how to solve it. The message I am getting is as followed:

This resource is present in the OPF <Manifest>, but its not reachable (it's unused).

What does this exactly mean and how do I fix it?? It lists this error message with each jpg.

Some of your problem can occur because in Windows case generally doesn't matter, but in epubs it does. Your problem could be a simple as Style, versus style, or an extra space in a file name...good reason to make them one word.

Many readers will not validate the epub, but if it is submitted to a publisher it may well be validated causing headaches for your client. If it is an in-house publication it doesn't matter, but tracking down what it was could be useful for your education...if not for your sanity! (grin)